From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-f198.google.com (mail-qt1-f198.google.com [209.85.160.198]) by kanga.kvack.org (Postfix) with ESMTP id 244F86B2325 for ; Tue, 20 Nov 2018 20:59:58 -0500 (EST) Received: by mail-qt1-f198.google.com with SMTP id n95so2038408qte.16 for ; Tue, 20 Nov 2018 17:59:58 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id p19si169695qvc.3.2018.11.20.17.59.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 Nov 2018 17:59:57 -0800 (PST) Date: Tue, 20 Nov 2018 20:59:43 -0500 From: "Michael S. Tsirkin" Subject: Re: [PATCH v1 3/8] kexec: export PG_offline to VMCOREINFO Message-ID: <20181120205822-mutt-send-email-mst@kernel.org> References: <20181119101616.8901-1-david@redhat.com> <20181119101616.8901-4-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181119101616.8901-4-david@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, devel@linuxdriverproject.org, linux-fsdevel@vger.kernel.org, linux-pm@vger.kernel.org, xen-devel@lists.xenproject.org, kexec-ml , pv-drivers@vmware.com, Andrew Morton , Dave Young , "Kirill A. Shutemov" , Baoquan He , Omar Sandoval , Arnd Bergmann , Matthew Wilcox , Michal Hocko , Lianbo Jiang , Borislav Petkov , Kazuhito Hagio On Mon, Nov 19, 2018 at 11:16:11AM +0100, David Hildenbrand wrote: > Right now, pages inflated as part of a balloon driver will be dumped > by dump tools like makedumpfile. While XEN is able to check in the > crash kernel whether a certain pfn is actuall backed by memory in the > hypervisor (see xen_oldmem_pfn_is_ram) and optimize this case, dumps of > other balloon inflated memory will essentially result in zero pages getting > allocated by the hypervisor and the dump getting filled with this data. > > The allocation and reading of zero pages can directly be avoided if a > dumping tool could know which pages only contain stale information not to > be dumped. > > We now have PG_offline which can be (and already is by virtio-balloon) > used for marking pages as logically offline. Follow up patches will > make use of this flag also in other balloon implementations. > > Let's export PG_offline via PAGE_OFFLINE_MAPCOUNT_VALUE, so > makedumpfile can directly skip pages that are logically offline and the > content therefore stale. > > Please note that this is also helpful for a problem we were seeing under > Hyper-V: Dumping logically offline memory (pages kept fake offline while > onlining a section via online_page_callback) would under some condicions > result in a kernel panic when dumping them. > > Cc: Andrew Morton > Cc: Dave Young > Cc: "Kirill A. Shutemov" > Cc: Baoquan He > Cc: Omar Sandoval > Cc: Arnd Bergmann > Cc: Matthew Wilcox > Cc: Michal Hocko > Cc: "Michael S. Tsirkin" > Cc: Lianbo Jiang > Cc: Borislav Petkov > Cc: Kazuhito Hagio > Signed-off-by: David Hildenbrand Acked-by: Michael S. Tsirkin > --- > kernel/crash_core.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c > index 933cb3e45b98..093c9f917ed0 100644 > --- a/kernel/crash_core.c > +++ b/kernel/crash_core.c > @@ -464,6 +464,8 @@ static int __init crash_save_vmcoreinfo_init(void) > VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE); > #ifdef CONFIG_HUGETLB_PAGE > VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR); > +#define PAGE_OFFLINE_MAPCOUNT_VALUE (~PG_offline) > + VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE); > #endif > > arch_crash_save_vmcoreinfo(); > -- > 2.17.2